1. Field of the Invention
The invention relates to the field of image guided therapy and to systems and methods for creating and utilizing phantoms for characterizing imaging errors to facilitate correction of such errors.
2. Description of the Related Art
Image Guided Therapies (IGT) refers to a wide range of existing and developing treatment modalities that employ one or more imaging technologies to assist more effective delivery of the related therapy. IGT can include but is not limited to such treatment modalities as image guided surgery, radiosurgery, radiotherapy, and other existing and developing types of therapy. In general, IGT utilizes one or more imaging technologies to gather information indicative of the internal structures and/or condition of tissue of interest. Image data is obtained that is generally manipulated by a computer system and associated applications software to generate and display a three dimensional virtual model or image of the imaged region. The image data can be used to more accurately locate regions of interest in space to facilitate more accurate and focused delivery of therapy to the regions of interest.
In many applications, the safety and efficacy of an IGT being used is dependent on the spatial accuracy of a 3D imaging system. For example, certain IGTs are directed to locating specific treatment regions or volumes and accurately delivering the appropriate therapy to the identified target. Errors in accurately identifying the spatial location of a desired target region can compromise the ability to accurately deliver the appropriate therapy. This can at best compromise the efficacy of the intended therapy by misdirecting the therapy and in some applications can have safety concerns, for example by unintentionally delivering the therapy to non-target regions.
A variety of imaging technologies can be used in IGT, however all known imaging technologies suffer from some degree of spatial distortion. Magnetic Resonance Imaging (MRI) utilizes a powerful magnetic field that is applied to an imaging space to preferentially align nuclear magnetization vectors, generally hydrogen atoms in water present in the tissue. Radio frequency fields are applied to alter the alignment of this magnetization thereby inducing perturbations in the magnetic field that are detectable by the MRI system. However, location data obtained via MRI systems is subject to spatial distortion from magnetic field distortions as well as chemical shifts that may occur within the imaging volume.
Computed Tomography (CT) is another type of imaging technology that utilizes computer processing to generate a virtual three dimensional image object by analyzing a generally large plurality of two dimensional x-ray images taken from different perspectives. However, CT imaging is also subject to distortion from a phenomenon known as beam hardening.
Single photon emission computed tomography (SPECT) and positron emission tomography (PET) are nuclear medicine imaging technologies that utilize radioactive tracer materials and detection of gamma rays to produce three dimensional images, frequently indicative of functional processes in the living body. In general, the tracers selected for use in SPECT systems emit gamma radiation that is detected directly whereas tracers selected for use in PET systems emit positrons which annihilate with electrons generally within a few millimeters inducing two gamma photons to be emitted and subsequently detected. SPECT and PET systems are subject to spatial distortion from such factors as attenuation and/or scatter of the gamma rays or gamma photons.
As previously noted, efficacy and safety of IGT is dependent on the accuracy of the imaging technologies used. It will thus be appreciated that there exists an ongoing need for improved systems and methods of more accurately imaging an image volume. There is also a need for characterizing spatial distortions present in an existing, or yet to be developed, imaging system.